1. Field of the Invention
In recent years, shrinking of a CMOS-type semiconductor device is being promoted in compliance with the request for the high-speed operation and the high-performance of the device. In accordance with progress in the shrinking, the scaling of the distance between the gate and the source/drain contact is required.
2. Description of the Related Art
The problems relating to the shrinking of the high-performance MOS transistor equipped with a silicide electrode will now be described.
FIG. 1A is a cross-sectional view showing the construction of a high-performance MOS transistor equipped with a silicide electrode. The MOS transistor shown in FIG. 1A comprises a Si substrate 101, a device isolation insulating film 102 of a shallow trench isolation (STI), a gate electrode formed of a polycrystalline silicon (polysilicon) film 106 formed on the Si substrate 101 with a gate insulating film 105 interposed therebetween, a shallow source/drain diffusion layer 107 formed by ion implantation with the gate electrode used as a mask, a gate side-wall insulating film 109 formed on the side-wall of the gate electrode, a deep source/drain diffusion layer 111 of a high impurity concentration formed by ion implantation with the gate electrode equipped with the gate side-wall insulating film 109 used as a mask, and a metal silicide layer 112 such as a cobalt silicide layer formed on the exposed surface of the deep source/drain diffusion layer 111 of a high impurity concentration and on the gate electrode formed of the polysilicon layer 106. A mark S1 shown in FIG. 1A denotes the length showing the expansion in the direction of the gate length of the metal silicide film covering the deep source/drain diffusion layer 111 of a high impurity concentration.
In shrinking the semiconductor device, it is absolutely necessary to decrease the width of the gate side-wall insulating film 109 in accordance with the scaling. Also, it is necessary to increase to some extent the depth of the deep source/drain diffusion layer 111 of a high impurity concentration in view of the generation of the leakage current in the junction surface between the deep source/drain diffusion layer 111 of a high impurity concentration having the silicided surface and the Si substrate 101. If the width of the gate side-wall insulating film 109 is decreased in this case, it is impossible to suppress the short-channel effect produced by the deep source/drain diffusion layer 111 of a high impurity concentration, with the result that it is difficult to shrink the width of the gate side-wall by the scaling in the high-performance MOS transistor equipped with a silicide electrode.
On the other hand, if the distance S1 between the edge of the gate side-wall insulating film 109 and the peripheral portion on the side of the source/drain of the device isolation insulating film 102 of STI is decreased by the scaling, the area of the metal silicide layer formed on the deep source/drain diffusion layer of a high impurity concentration is decreased so as to increase the parasitic resistance. Particularly, in the case of using the MOS transistor structure of a corner contact type, in which a contact hole is formed in the corner portion of the source/drain forming region, the increase in the parasitic resistance constitutes a serious problem.
In conjunction with the problem described above, the method of forming a contact hole for connecting the source/drain regions of a high-performance MOS transistor equipped with a silicide electrode to the wiring on the semiconductor substrate and the problems accompanying the forming method will now be described in detail with reference to FIG. 1B.
FIG. 1B is a cross-sectional view showing the step of forming a contact hole in a high-performance MOS transistor equipped with a silicide electrode. As shown in the drawing, an interlayer insulating film 118 is formed to cover a high-performance MOS transistor equipped with silicide electrodes isolated from each other by the device isolation insulating film 102 of STI, followed by forming a contact hole 119 in the interlayer insulating film 118 by aligning a mask with the metal silicide layer 112 on the deep source/drain diffusion layer of a high impurity concentration by using a resist (not shown) and lithography.
In this case, if the length S1 shown in FIG. 1A is shrunk by the scaling, a mask misalignment is generated as shown in FIG. 1B, with the result that the contact hole 119 partly reaches the gate side-wall insulating film 109 so as to markedly decrease the distance S2 corresponding to the contact area with the metal silicide layer 112.
The connection between the metal wiring (not shown) on the semiconductor substrate and the metal silicide layer 112 is achieved by burying a contact plug made of a metallic material in the contact hole 119. Therefore, if the distance S2 is decreased, the parasitic resistance between the source and drain of the MOS transistor is increased so as to lower the operating speed.
Also, with progress in the development of the semiconductor device, it is necessary to make shallower not only the shallow source/drain diffusion layer 107 of the MOS transistor but also the deep source/drain diffusion layer 111 of a high impurity concentration. However, as described previously, if the source/drain diffusion layer 111 of a high impurity concentration is made shallower, the generation of the contact leakage in forming the silicide layer 112 and the increase in the power consumption of the CMOS circuit accompanying the generation of the contact leakage are brought about as new problems. As a measure for overcoming these problems, proposed is a MOS transistor of an elevated source/drain structure.
The MOS transistor of this type is constructed such that a single crystal Si or SiGe layer is formed selectively by means of an epitaxial growth on a source/drain diffusion region of a high impurity concentration, and the impurity concentration in the surface region of the Si substrate including the epitaxial growth layer is increased so as to make the high impurity concentration diffusion layer in the Si substrate substantially shallower.
In the case of using the elevated source/drain structure, the surface region of the single crystal Si or SiGe layer grown by the selective epitaxial method on the source/drain diffusion region is converted into a silicide region so as to make it possible to avoid the generation of the contact leakage current.
In applying the elevated source/drain structure, it is absolutely necessary in allowing the CMOS circuit to operate normally to ensure the device isolation characteristics of STI so as to prevent completely a single crystal Si or SiGe layer from growing on the upper surfaces of the device isolation insulating film 102 of STI and the gate side-wall insulating film 109 and to allow the epitaxial growth layer to be formed selectively only on the upper surface of the source/drain diffusion region.
However, in the STI having a small separation width, the buried state is rendered poor when the device isolation insulating film 102 is buried in the trench so as to generate a seam of the device isolation insulating film in the central portion of the trench width in the longitudinal direction of the trench, as described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 58-143548 and Jpn. Pat. Appln. KOKAI Publication No. 1-151245. In this case, if the epitaxial growth layer is selectively formed on the source/drain diffusion region, Si or SiGe particles are generated in the central portion in the width direction of the STI with the portion of the seam providing the growth nucleus.
The failure generation of the device isolation characteristics in the elevated source/drain structure will now be described more in detail with reference to FIGS. 2A and 2B. FIG. 2A is a cross-sectional view showing the normal STI structure in the elevated source/drain structure. The device isolation insulating film 102 of STI shown in FIG. 2A is buried satisfactorily in the trench because the trench has a large width, with the result that a seam generation is not recognized in the central portion of the STI. It follows that, if an epitaxial growth layer 110 is selectively formed on the Si substrate 101, the epitaxial growth layer 110 is formed in the peripheral portion of the device isolation insulating film 102 in which the STI is contiguous to the Si substrate 101. However, since a Si layer is not grown in the central portion of the device isolation insulating film 102, good device isolation characteristics can be assured.
However, if the trench width is small as shown in FIG. 2B, a device isolation insulating film 116 fails to be buried satisfactorily in the trench, with the result that a seam 117 of the device isolation insulating film 116 is generated in the central portion of the trench width in the longitudinal direction of the trench. In the surface of the device isolation insulating film 116 in which is generated the seam 117, the surface selectivity with the surface of the Si substrate is lowered in the process of the epitaxial growth, with the result that Si or SiGe particles 110a are generated with the seam 117 providing the nucleus of the growth. As a result, the leakage current on the surface of the device isolation insulating film 116 is increased so as to lower the device isolation characteristics of the STI, leading to the occurrence of a short-circuit. Incidentally, the deep source/drain diffusion layer 111 of a high impurity concentration is omitted from each of FIGS. 2A and 2B so as to simplify the drawing.
As described above, the performance of the MOS transistor is improved in the prior art by utilizing the elevated source/drain structure. However, since it is difficult to shrink the gate side-wall insulating film by means of scaling, the area of the contact on the source/drain region is decreased so as to give rise to the problem that the connection to the wiring by the contact hole is rendered difficult.
It should also be noted that, in accordance with the shrinking of the STI, a seam is generated in the device isolation insulating film when the device isolation insulating film is buried in the trench, with the result that, if a Si or SiGe layer is formed by a selective epitaxial growth method on the source/drain diffusion layer, Si or SiGe particles are generated on the device isolation insulating film with the seam providing the nucleus of the growth so as to give rise to the problem that the device isolation characteristics of the STI are degraded.
Each of the embodiments of the present invention described below provides a semiconductor device that permits assuring the contact area on the source/drain region regardless of the shrinking of the transistor structure by the scaling and a method of manufacturing the particular semiconductor device. Each of the embodiments of the present invention also provides a semiconductor device that permits assuring a high surface selectivity between the surface of the device isolation insulating film buried in the STI and the surface of the substrate on the source/drain diffusion layer so as to make it possible to realize an elevated source/drain structure while maintaining good device isolation characteristics of the STI and a method of manufacturing the particular semiconductor device.